The field covers the structure of a ported cylinder of an opposed-piston engine. More specifically the field is directed to a liner component with cooling passageways and stiffening members defined by a ring of powdered material encircling the liner.
With reference to FIG. 1, an opposed-piston engine includes at least one cylinder in which pistons 20, 22 move in opposition. As taught in related U.S. Pat. No. 8,485,147, a cylinder for an opposed-piston engine includes a liner 10 having a bore 12 and longitudinally displaced exhaust and intake ports 14, 16 that are machined or formed therein. One or more injector ports 17 open through the side surface of the liner. The two pistons 20 and 22 are disposed in the bore 12 with their end surfaces 20e, 22e in opposition to each other. In a compression stroke, the pistons move toward respective top center (TC) locations where they are at their innermost positions in the cylinder. When combustion occurs, the pistons move away from TC, toward respective ports. While moving from TC, the pistons keep their associated ports closed until they approach respective bottom center (BC) positions where they are at their outermost positions in the cylinder. An annular portion 25 of the liner surrounds the bore volume within which combustion occurs, that is to say, the portion of the bore volume in the vicinity of the piston ends when the pistons are at or near TC. For convenience, that portion of the liner is referred to as the “TC” portion. While the engine runs the TC portion 25 is subject to extreme strain from the temperatures and pressures of combustion. Consequently, there is a need for structural reinforcement and cooling measures at the TC portion 25 to mitigate the effects of combustion.
The '147 patent describes a cylinder structure in which the liner is provided with an annular reinforcing band encircling the TC portion of the liner sidewall and a metal sleeve received over the TC portion of the liner. The reinforcing band provides hoop strength to resist the pressure of combustion. Grooves disposed between the metal sleeve and the liner provide channels for a liquid coolant. Longitudinal coolant passageways drilled in the liner extend through bridges in the exhaust port to transport liquid coolant from the grooves. The grooves conduct liquid coolant from the vicinity of the reinforcing ring toward the ports; the drilled passageways provide an added measure of cooling to the exhaust port.
Manifestly, an opposed-piston cylinder liner presents unique engineering and manufacturing challenges. The thin exhaust port bridges are exposed to very hot exhaust gases during engine operation and consequently require coolant flow to maintain structural integrity. Furthermore the combustion volume of the cylinder, particularly in the annular TC portion of the liner, requires additional strength and coolant flow to withstand the extreme temperatures and high pressures of combustion.
One procedure for producing the coolant passageways through the exhaust port bridges includes gun drilling; see the above-referenced '147 patent, for example. According to another procedure, slots are machined or cast in the port bridges and then covered with a metal ring that is press-fit, welded soldered, or brazed to attach the ring to the liner. In this regard, see for example, U.S. Pat. No. 1,818,558 and U.S. Pat. No. 1,892,277. The high-pressure TC portion of the liner where combustion occurs may have grooves formed in the outer surface of the liner for coolant passages which are covered by a press-fit hard steel ring or sleeve to enclose the coolant and relieve hoop stress in the TC portion of the sleeve. In this regard, see U.S. Pat. No. 1,410,319, and the above-referenced '147 patent. All of these structures have limitations. Cold press-fit joints require precision manufacturing, extra components and precision assembly, all of which result in high cost. Welded joints change the microstructure of the joined pieces in local areas, thereby changing tempering and mechanical properties that can increase failure and scrap rates. Soldered or brazed joints include substrate material that can decay over time with varying results. Materials that are able to withstand the exhaust temperatures are expensive.